Reading a List of Data into a Function Using a Script
My job requires the managing of large amounts of files and data (about 6500 files/items per query/set). Managing and querying such large amounts of data by hand is impossible and a waste of time when you can have a KornShell script do this for you. This tech-recipe is just an example of what you can do with some variables, menus, and functions.
Overview: In this tutorial, I will give a few sample scripts and explain how each works. From there, you can hopefully use the fundamental concepts in each and apply it to your own area/field/use. However, there is more going on in each of my examples than just the script. You also have to be sure that the way you are setting up the data to be queried is going to work. (Take for instance an example in which we have 100 customers who are identified in our system by a 5 digit customer number. Be sure to keep the data structure for them consistent. When you go back to write a script to query the data, it makes the process much easier). Functions are not executed until called within the script.
Creating a Script that Uses a Function to Call in a List of Data
Copy the text in the quote below to a file named script.ksh.
Then create list.txt file in the same folder with these numbers on a line:
Then create three text files with the same name as number in the the list. (i.e., 1.txt, 2.txt, 3.txt). Put different data in each.
# basic script that uses a function to call in a list of data to then query
# creates function called readDATA
#main script that will call function
echo “Test Script: Read Data from List, test.txt”
while read -r data
done < list.txt
Here is what each script is doing:
The first thing we did was create the function. A function is basically just a mini-script within a script that you can call at any time. The function we set up is just going to echo the contents of the file $data.txt to the screen.
The next thing we set up was the while statement to execute the script.
This will read the list file, list.txt. Then for each line in the list.txt, it will temporarily assign it to be the $data variable and send that variable through the function.
Let’s see it in action.
while -r read (using our list from above of 1, 2 , 3 on separate lines)
the first time through it would see the read = 1
It then passes the 1 value to the readDATA function.
It then translates the $data variable to 1 and will echo 1.txt to the screen.
The script will keep running through the file until it reaches the end of the file. ( done < list.txt defines this.)
This is a basic script and usagee of reading from a list. I have a script I use at work that allows me to define the list files and also have more than one variable per line and so on. Understanding how to read the data from a list and how functions work was a great way for me to really start to understand the power of ksh.
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